Support Convolution&Batchnorm Fusing for Optimized Inference Mode

[DonghakPark]

One of the ways to accelerate running the NNTrainer in inference mode is to fuse operations. We are currently using this fusion when exporting to TensorFlow Lite. By applying it to the current NNTrainer, we can improve the speed during inference.

Many Deeplearning Model using Batchnorm after Conv layer

and when inference we can fusing ops to below

image ref